Others have already covered it, but if you think about it, not everything is an object. In computing, nothing is truly an object. We just abstract out the concept of an object.
For example, rocks are composed of matter. We could think of rocks as objects in computing terms (OOP terms) but that doesn't help programming around the concept of a rock.
If you think about the main concepts of object oriented programming; encapsulation, polymorphism, classes, inheritance.. there are problems with all of those core OOP concepts.
